1. Field of the Invention
The present invention relates to digitally controlled solenoid actuator fluid control valves.
2. Description of Related Art
Control valves are typically used to control the flow of fluid within an hydraulic or pneumatic system. Some conventional fluid control valves contain a solenoid(s) which moves a spool within the inner chamber of a valve housing. The fluid is routed between various housing ports in accordance with the position of the spool. Conventional control valves include two-way, three-way and four-way valves. A two-way valve contains two ports and provides fluid communication between the two ports when in an open position and blocks the flow of fluid between the ports when in a closed position.
A three-way valve allows fluid communication between a first port and a common port when the spool is in one position and allows fluid communication between a second port and the common port when the spool is in a second position. By way of example, the first port can be connected to the outlet of a pump, the second port can be connected to a drain and the common port can be coupled to a cylinder chamber of an actuator. When the solenoid of the control valve is energized, the spool allows fluid to flow from the pump to the actuator, causing an output shaft of the actuator to move into an extended position. When the solenoid is de-energized, a return spring moves the spool back to the original position so that the cylinder chamber of the actuator is in fluid communication with the drain. The actuator may also have a return spring which moves the output shaft back to the original position and pushes the fluid within the cylinder chamber to the drain through the control valve. The control valve can thus be used to extend and retract the output shaft of an actuator.
A four-way valve couples a pair of fluid ports with a second pair of fluid ports, in accordance with the position of the spool. Four-way valves are particularly useful in controlling actuators which do not have spring return output shafts. For example, the supply port of a four-way valve may be connected to a pressurized fluid supply, the return port may be connected to drain, a first cylinder port may be coupled to a first cylinder chamber of the actuator and a second cylinder port may be coupled to a second opposite cylinder chamber of the actuator. When the spool is in one position, the spool couples the first cylinder chamber to the supply port and the second cylinder chamber to drain. When the spool is moved into the second position, the spool couples the first cylinder chamber to drain and the second cylinder chamber to the supply port. Like the three-way valve, a four way valve can both extend and retract the output shaft of an actuator.
Conventional solenoid actuated control valves are analog in the sense that power must be continuously supplied to energize the solenoid. The continuous supply of power generates heat which can degrade the performance and life of the coil wires and the valve. Analog valves are typically constructed to compensate for the heat by increasing the size and mass of the valve. Bulky heavy control valves are undesirable for applications such as the control of fuel in an automobile, where size and weight are critical. It is desirable to have a control valve that does not require power to maintain the spool of the valve in either position. It is also desirable to provide a solenoid control valve, which is reliable, relatively inexpensive to produce, has a quick response time and can be operated without a continuous supply of power.